<p id="birthdistrictbox">
    <select id="birthprovince" name="birthprovince" class="form-control w_300"  onchange="showdistrict(this.selectedIndex)"></select>
    <select id="birthcity" name="birthcity" class="form-control w_300"></select>
    <select id="birthdist"  name="birthdist" class="form-control w_300"></select>
</p>